Copper (Cu) is a representative nonferrous metal which exhibits superior alloy properties, and copper materials to which a variety of ingredients are added according to the intended purpose are widely used in various fields. Copper and copper alloy materials are roughly classified into plate materials, rods, tubular materials and castings. Such a material is used for a variety of products or materials via the post process. For example, phosphorous bronze, that is produced by adding less than 1% by weight of phosphorous (P) in order to reinforce hardness and strength of copper alloys and to improve corrosion resistance, is used for processed materials such as plates and cables requiring high elasticity, and is used for castings of pump components, gears, ship components, chemical mechanical components and the like. Also, aluminum bronze in which a small amount of aluminum (Al) is added to copper (Cu) was not utilized in general applications due to problems such as melt-casting or self-annealing and the application thereof gradually extends in accordance with metallographic requirements and melt-casting techniques' improvement. Strength brass, called “Manganese (Mn) bronze” is obtained by alloying brass with 1 to 3% by weight of manganese, and can satisfy requirements such as strength, corrosion resistance and seawater resistance when elements such as aluminum (Al), iron (Fe), nickel (Ni), tin (Sn) and so on are added thereto.
In addition, copper (Cu) has a high elongation to the extent that it can be processed into thin plates or fine cables. As an elongation increases, the parent metal is stuck on a tool during a cutting process, a great amount of heat is generated, and cutting processability is deteriorated, for example, the processed surface is roughened and lifespan of the tool is shortened. An alloy that solves these problems and exhibits improved cutting processability is referred to as a free-cutting copper alloy. At present, a copper alloy to which free-cutting property is imparted by adding 1.0 to 4.1% by weight of lead (Pb) to a brass alloy is widely used throughout the overall industry and living life.
However, since Restriction of Hazardous Substances (RoHS) was established by law in Europe in 2003, environmental regulations have been tightened up, regulations of elements hazardous to human health have been implemented, and research associated with a novel alloy that serves as a substitute for a free-cutting copper alloy that exhibits improved machinability based on addition of lead (Pb) has been made. In order to obtain machinability comparable to lead, brass alloys to which bismuth (Bi), selenium (Se), or telenium (Te) is added were developed. Although whether or not bismuth (Bi) is harmful to human health is not clear, bismuth (Bi), as a heavy metal such as lead (Pb), may be restricted in futures. Also, selenium (Se) and telenium (Te) are very expensive and are thus considerably unsuitable for general industrial applications. Also, since lead (Pb) and bismuth (Bi) entail high costs due to difficulty of recovery through general smelting and refining, need high energy when recovered by a physical method, and cause defects such as cracking during hot processing, used in a small amount in combination with a general copper alloy (see, reference document 1), thorough management of scrap is required for recycling of lead and bismuth.
In an attempt to resolve detriments of human and solve the problems associated with recycling of lead (Pb) and bismuth (Bi), alloys in which calcium (Ca) is added to brass have been developed (see Reference document 2). However, alloys exhibited insufficient hot processability, low dezincification resistance and thus insufficient corrosion resistance.